1. Field of Invention
This invention relates to novel compositions of matter useful as crosslinking agents in melt-processable and radiation crosslinkage polymer compositions.
2. Description of the Prior Art
It has been proposed to irradiate fluorocarbon polymers and other high temperature polymers to improve their mechanical properties at elevated temperatures. Suitable ionizing radiation includes gamma rays and accelerated electrons. As a rule, degradation, rather than crosslinking, predominates when such polymers are subjected to melt treatment. Frequently, heating or annealing of such polymers subsequent to irradiation is said to improve their mechanical properties. It has also been reported that small amounts of unsaturated compounds such as triallyl cyanurate (TAC) or its isomer, triallyl isocyanurate (TAIC), function in such polymers, especially fluorocarbon polymers, as a crosslinking promoter during exposure to radiation.
It has also been reported that fluorocarbon polymer compositions containing relatively volatile crosslinking promoters e.g., TAC or TAIC, cannot be melt processed, such as by extrusion or injection molding, when the polymeric composition requires a processing temperature above about 250.degree.. For a variety of polymers, such temperatures are needed to fabricate shaped articles such as wire insulation, sheets, film, tubing, gaskets, and boots. Polymer compositions containing prior art crosslinking agents tend to prematurely crosslink and to form gels or lumps, discolor and often to form voids in the final product. For example, as set forth in detail in U.S. Pat. Nos. 3,763,222; 3,840,619; 3,894,118; 3,911,192; 3,970,770; 3,985,716; 3,995,091 and 4,031,167 it is seen that substantial difficulty has been experienced in providing heat stable crosslinking agents suitable for use with fluorocarbon polymers that demonstrate low volatility and high crosslinking efficiency. In fact, no single compound, or mixture of compounds, has provided the unique combination of properties, such as low volatility, high polymer compatibility, high thermal stability and high unsaturation content, required to produce high crosslinking efficiencies in melt processed polymer compositions. All known prior art compounds suffer from one or more dificiencies, e.g., poor polymer compatibility or poor chemical stability, which lead to inferior polymer products that contain heterogeneities, decomposition products or discoloration which demonstrate undesirably low mechanical performance. There is no known crosslinking agent which provides entirely satisfactory properties in melt processed, high temperature polymer compositions. We have now unexpectedly discovered that the above deficiencies can be obviated by the use of certain crosslinking agents and their novel compositions in polymers as described hereinafter.